A thermoplastic dispersion type fluororesin coating material composed mainly of a polyvinylidene fluoride or a solvent soluble type thermosetting fluororesin coating material composed mainly of a copolymer of a fluororesin with a vinyl ether or a vinyl ester, has been widely used in recent years in the coating material field e.g. for heavy duty corrosion prevention, building or industrial application by virtue of corrosion resistance, weather resistance, durability, stain-removal properties, etc. of the coating film (e.g. JP-B-60-21667, JP-A-59-102962, JP-A-61-57609, etc.).
Further, in view of an environmental pollution problem which has been increasingly serious year after year, a powder fluororesin coating material which is a non-solvent type coating material having the discharge amount of an organic solvent (VOC) reduced, has been proposed (e.g. JP-A-1-103670, JP-A-2-60968, JP-A-6-345822, JP-A-7-145332, etc.).
Usually, a powder coating material is produced by producing and then roughly pulverizing the main material resin, dry blending a curing agent or various additives thereto, followed by melt-kneading, repulverization and classification.
A fluororesin coating material is excellent in weather resistance, etc, as mentioned above, but the glass transition temperature (hereinafter sometimes referred to simply as Tg) of the fluororesin to be used as the main material resin is relatively low at a level of from −40 to 50° C. in many cases. If Tg is low like this, there will be a problem that blocks will form during the storage of the powder coating material, i.e. blocking will result. Whereas, it has been proposed to obtain a fluororesin having high Tg by copolymerizing a monomer such as vinyl benzoate. However, if Tg is made too high, the melting temperature at the time of coating will be too high, thus causing another problem such that smoothness of the coating film will be impaired. Further, a monomer such as vinyl benzoate is expensive thus leading to an increase of the cost, and if this proportion is made large, the weather resistance decreases.
It is an object of the present invention to solve such problems of the prior art and to provide a fluororesin powder coating composition excellent in both smoothness of the coating film when coated and storage stability, without impairing the characteristics such as weather resistance inherent to a fluororesin coating material.